The present invention relates to a tire wheel for vehicles, i.e. to the assembly comprising a mounting rim designed for connection to a hub of the vehicle itself, a tire mounted on said mounting rim and an inner tube inserted inside said tire, designed to be inflated with a fluid under pressure via a special inflating device.
More particularly, the invention relates, albeit not exclusively, to a tire wheel for use on motor vehicles with very high performance features, i.e. vehicles which are able to produce a high driving torque and reach high speeds both along straight road sections and around bends.
The tire wheels of the type described must be able to satisfy fully various requirementsxe2x80x94also partly conflicting with one anotherxe2x80x94which are associated with the performance features required by the market today.
In particular they must be able to provide the vehicle with an excellent handling performancexe2x80x94particularly as regards the directional and transverse stabilityxe2x80x94, road-holding power and traction on any type of ground, resistance to aquaplaning, comfort, as well as the capacity to continue travelling over a reasonable distance also in the case of partial or total loss of air (run-flat conditions), without the risk of xe2x80x9cunseatingxe2x80x9d, i.e. the condition where one or both of the tire beads comes out of the associated seat formed on the rim.
The Applicants have noticed that, hitherto, these requirements have generally been satisfied individually by a single component from among those which make up the wheel: thus the handling has been attributed to the performance features of the tire, while the resistance to xe2x80x9cunseatingxe2x80x9d has been sought after by means of suitable shaping of the bead seats. As regards the so-called xe2x80x9crun-flat capacityxe2x80x9d, according to a first method, this has been obtained by modifying the carcass structure, strengthening the sidewalls of the tire so as to provide it with a self-supporting capacity; by way of an alternative, in tubeless tires this capacity has been provided by suitable supports mounted on the rim and inserted inside the tire, while in tires with inner tubes an air chamber, or inner tube, divided up into a plurality of circumferential or transverse compartments independent of one another has been used.
The presence of several independent compartments allows the tire to be provided with a sufficient inflation pressure, and hence capacity for emergency travel, even when one of said compartments has suffered a puncture.
It has been found that all these solutions, compared with the advantages offered, also have various disadvantages, such that the overall result obtained is penalized.
In particular, the Applicants have noticed that:
the increase in the structural rigidity of the sidewalls results in a greater weight of the tire and a greater rigidity thereof in all directionsxe2x80x94longitudinal, transverse and verticalxe2x80x94which has a negative effect on the driving performance under normal conditions, and on the comfort;
the use of a support inside the tire increases the weight of the tire and does not provide any guarantee as to long resistance during run-flat conditions, when the weight of the car is transmitted onto the support with frictional contact between the radially internal surface of the tire and the radially external surface of the support; and
the solution with inner tube is not practical with so-called low-profile tires, i.e. those tires which have an elliptical cross-section elongated along the axis of rotation, in which difficulties both as regards insertion and use are encountered.
The Applicants have been able to establish, in fact, that the insertion of the inner tube between tire and rim is all the more difficult the lower the cross-section of the tire. In addition to this, traditional inner tubes, during inflation, assume a profile which is substantially circular in cross-section and does not combine properly with the elliptical profile of the low-profile tire, resulting in folds which form on top of one another and prevent correct and complete extension of the walls of the inner tube onto the internal surface of the toroidal cavity, in particular along the sidewalls of the tire. In this way the toroidal cavity is not filled properly and a damaging state of internal tensions in the wall of the inner tube arises, adversely affecting the duration thereof.
Furthermore, as perceived by the Applicants, further problems are associated with the fact that traditional inner tubes are provided with an inflating valve comprising a stem which passes through the rim for connection to the external environment outside the wheel. In particular travel conditions of the tire, this fact represents a risk which at present has not yet been eliminated: it has been found that, in the case of sudden accelerations or decelerations of the vehicle, such as those which are produced by high-performance vehicles which transmit to the ground very high torque values, slipping of the tire with respect to the rim may occur, with consequent tearing of the inner tube at the base of the valve or shearing of the valve stem. When this occurs, there is an immediate deflation of the tire and associated loss of stability of the vehicle, with serious danger for the lives of the driver and passengers of the vehicle itself.
Even the most recent proposition to improve the behaviour of the abovementioned tire wheels as regards the run-flat capacity, and resistance to unseating has not diverged from the known art, envisaging a solid insert inside the cavity defined by the rim and tire assembly.
For the sake of convenience of the description, it is pointed out here that this assembly has a mounting rim which is provided with conical bead seats whose axially external end has a diameter less than that of the axially internal end and is associated with a radial carcass tire, the beads of which match the corresponding seats on the rim while the carcass has a meridian profile, in cross-section, with a constant direction of curvature, the tangent of which, in the vicinity of the bead cores, is substantially parallel to the equatorial plane.
In the embodiment proposed, the rim has bead seats of different diameter and the bead seat of larger diameter is delimited in an axially internal position by a shoulder which is of considerable height so as to prevent unseating on that side, but is difficult to pass over. The wheel is completed with a tread support ring radially extending over about half the cross-section height of the tire: the ring is fitted onto the rim, in the vicinity of the bead seat of smaller diameter and, in the event of deflation of the tire, locks in position the adjacent bead, preventing unseating of the tire on the corresponding side. This wheel is described in detail for example in U.S. Pat. No. 5,634,993, to which reference should be made for further information.
The Applicants have realized that this solution is also not completely satisfactory in relation to the high standards of quality and performance which are nowadays required by the market, i.e. by vehicle manufacturers, by tire retailers and by the users themselves. In particular they have perceived that the version without tread support results in the return to tires with reinforced self-supporting sidewalls, while the internal solid support ring reduces the volume of inflating air which is already small in low-profile tires, thereby reducing the comfort, limits the vertical deformability of the tire, adversely affecting the driving performance, increases the thermal mass forming a harmful barrier against the dissipation of the heat produced during use, and requires a particular constructional form of the rim, which results in the need for a different diameter of the bead seats of the rim, making assembly and disassembly of the ring in particular, and the wheel assembly in its entirety, difficult.
All this having been stated, the Applicants have now discovered that the performance characteristics of a vehicle tire wheel may be further improved by using an assembly of partly known and partly new elements, which forms a tire system capable of developing a mutual interaction between them, resulting in a new vehicle tire wheel which satisfies at the same time and in an optimum manner the performance characteristics required by modern vehicles.
The aforementioned wheel comprises essentially a wheel rim with bead seats which are inclined towards the axis of rotation, proceeding axially outwards away from the equatorial plane; a tire provided with beads externally shaped in the manner of the corresponding seats on the rim and with a carcass profile, viewed in cross-section, which has its maximum axial width in the region of said beads which are preferably formed with a new structure for fixing the carcass ply to the bead reinforcing core; and an inner tube, which preferably has an elliptical cross-section and which can be inflated by means of an inflation device which does not have any element for connection to the environment outside the wheel, in particular passing through the wall of the rim.
According to a first aspect thereof, the invention therefore relates to a tire wheel for vehicles, comprising a mounting rim which can be associated with a hub of said vehicle, a tire mounted on said rim and comprising a toroidal carcass provided with a crown portion connected to a pair of axially facing sidewalls terminating in beads for engagement with corresponding bead seats formed on the mounting rim, said carcass being provided with at least one reinforcing ply extending from bead to bead, with its ends fixed to reinforcing bead cores inserted inside said beads, the assembly of said tire and said rim defining a toroidal cavity which can be isolated from the surrounding environment at atmospheric pressure, and an inner tube which is inserted in said cavity and can be elastically expanded by means of the introduction of fluid under pressure into its internal volume and is provided with an inflating and deflating device which is inserted in the wall of said inner tube, said wheel being characterized in that:
said rim comprises a substantially cylindrical body, the axis of which forms the axis of rotation of said wheel, the radially external surface of said body having two side portions designed to form said bead seats for engagement with corresponding beads of said tire, each arranged according to a conical surface with its apex on said axis of rotation in a position axially outside said seat with respect to said rim, and a radially more inward central portion with a maximum diameter less than the minimum diameter of said conical side portions;
said tire has a width in the region of said beads at least equal to its maximum width in the region of said sidewalls;
said device does not have any system for connection to said rim, designed to fix the circumferential position of said inner tube with respect to the rim.
The abovementioned tire wheel is provided, on the rim, with means for introducing and removing fluid under pressure respectively into and from the toroidal cavity defined between tire and rim.
Preferably, the angle at the apex of said conical surfaces of the bead seats is between 8xc2x0 and 60xc2x0. The abovementioned bead seats are axially delimited towards the outside each by a flange diverging in a direction radially outside the rim and inclined with respect to the equatorial plane at an angle of between 40xc2x0 and 50xc2x0, while towards the inside they are each axially delimited by a shoulder, the axially external surface of which converges towards the equatorial plane in a direction radially outside the rim and is inclined with respect to said plane at an angle of between 0xc2x0 and 30xc2x0.
Even more preferably, the difference between the maximum diameter of said central portion, on the radially external surface of the abovementioned cylindrical body, and the minimum diameter of said bead seats is between 10% and 20% of said minimum diameter; the difference between the external diameter of said flange and the minimum diameter of the corresponding bead seat is between 1% and 5% of the value of said minimum diameter.
According to a second aspect thereof, the invention also relates to a tire wheel as described, in which the bead seats have a different distance from the axis of rotation of said wheel, where the difference between the minimum diameter of the bead seat of larger diameter and the maximum diameter of the bead seat of smaller diameter, which is axially opposite, is between 3% and 6% of the value of said maximum diameter.
Preferably, in this case, the rim is designed for mounting on the vehicle with the bead seat of larger diameter facing the vehicle itself.
According to a different aspect thereof, the invention relates to a tire wheel of the type described, fitted with a tire in which the bead reinforcing core comprises at least two radially superimposed layers of metal wires which are wound in turns arranged axially alongside one another and extending substantially over the entire axial extension of the corresponding bead seat and are arranged substantially parallel to the surface of the bead seat, where the minimum diameter of the radially innermost layer is not less than the diameter of the adjacent flange and its maximum diameter is not greater than the diameter of the adjacent shoulder.
The layers are preferably formed by high carbon content steel wires and may consist of a spiral of a single metal wire, with a diameter of between 0.9 mm and 1.5 mm, or a spiral of stranded metal cord where the basic filament of said strands has a diameter preferably of between 0.22 mm and 0.38 mm.
The bead core may comprise either layers consisting of basic filaments or layers of cords or a combination of said layers.
With this type of bead core, preferably the end of the carcass ply is inserted, axially from the inside outwards, between said layers.
In a preferred embodiment in which the end of said carcass ply comprises two axially separate portions of fabric, a first portion of fabric is arranged in position radially inside the radially innermost layer of metal wires, while the second portion of fabric is inserted in position radially inside the radially outermost layer of said wires, separated from the radially innermost layer by an insert of elastomeric material which extends radially beyond the axially internal end of said layers of metal wires towards the sidewall of the tire and which has a hardness of not less than 70xc2x0 Shore A.
According to a further aspect thereof, the invention relates to a tire wheel as described, in which the inner tube has been moulded and vulcanized with a toroidal shape having an internal volume not less than one third of the final volume of use, and has preferably been moulded and vulcanized with an elliptical shape.
Even more preferably, the inner tube comprises at least two circumferential volumes which are separate and independent of one another, being separated by a longitudinal wall extended in a plane perpendicular to the axis of rotation of the wheel, each volume being provided with said inflating device. Even more preferably, this wall has a rigidity which is greater than that of the axially outermost part, i.e. the sidewalls, of said inner tube. In addition or by way of alternative, this wall contains at least one duct which extends internally over the whole radial extension of the wall, opening out on both the extrados and intrados surfaces of the inner tube.
According to yet another aspect thereof, the invention relates to a tire wheel as described, in which said inflating and deflating device comprises a rigid body incorporating at least one inflating valve, one calibration valve and one discharge valve.